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Shigellosis -- United States, 1983

In 1983, 14,946 Shigella isolates from humans were reported to CDC. This is a 10.5% increase from the 13,523 isolates reported in 1982. The number of isolates is still less than the 15,334 reported during the peak year, 1978 (Figure 1).

Shigella serotypes were reported for 14,089 of the 14,946 isolates. The most frequently isolated serotype, S. sonnei, comprised 65.8% of all isolates serotyped (Table 1). When compared with 1982, the number of reported isolates increased notably in all serotypes except for S. flexneri, which remained relatively constant (Table 4). S. flexneri 1a accounted for 13.5% of all S. flexneri subtyped; 1b, 13.2%; 2a, 25.4%; 3a, 18.5%; and 6, 11.3%.

The reported increases in the number of isolates from specific serotypes were not confined to one state or region. However, from 1982 to 1983, reported S. sonnei isolates increased notably in Indiana (35 to 193), Maryland (85 to 199), Missouri (35 to 217), and New York (134 to 899). The increase in New York was associated with an outbreak in New York City.

The age-specific attack rate for persons from whom isolates were reported was highest for 2-year-old children, lower for older children, and lowest for adults. The age-specific attack rate for 20- to 29-year-olds was slightly higher than the attack rates for the older children and the remaining age groups (Figure 2). In addition, in the 20- to 29-year age group, a slightly higher isolation rate was reported for females than for males. The isolation rates by sex were similar for the remaining age groups.

Since some populations have a higher attack rate than others, data were tabulated separately for patients residing in certain institutions (e.g., nursing homes, facilities for the mentally ill, and other resident-care centers) and on American Indian reservations. Only 4,124 (27.6%) of the reports included data on residence at the time of onset of illness. Of those specified, 49 (1.2%) lived in institutions and 54 (1.3%) on Indian reservations. Forty-eight (97.8%) of the reported isolates from residents of institutions were S. sonnei, and one (2.0%) was S. flexneri. Thirty-four (63.0%) of the reported isolates from Indian reservation residents were S. sonnei and 20 (37%) were S. flexneri. For other known residences, S. sonnei accounted for 2,918 (74.4%); S. flexneri 936 (23.9%); S. boydii for 39 (1.0%); and S. dysenteriae for 27 (0.7%). Reported by Statistical Svcs Activity, Enteric Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC. Editoral Note: This report is based on CDC's Shigella Surveillance Activity, a passive laboratory-based system that receives reports from the 50 states and the District of Columbia. These reports do not distinguish between clinical or subclinical infections or between chronic or convalescent carriers.

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